Lipids Contribute to Heterochromatin Condensation Revealed by Quantitative Raman-Brillouin Microscopy.

Area of Science:

• Cell Biology
• Molecular Biology
• Biophysics

Background:

• Chromatin structure, comprising DNA and proteins, dictates genome accessibility and function.
• Heterochromatin and euchromatin represent distinct condensation states with differing transcriptional activity.
• The molecular drivers of heterochromatin condensation remain incompletely understood.

Purpose of the Study:

• To investigate the molecular composition of heterochromatin and its role in condensation.
• To explore the relationship between chemical constituents and mechanical properties of chromatin.
• To elucidate the dynamic regulation of heterochromatin formation.

Main Methods:

• Utilized label-free Raman-Brillouin microscopy for simultaneous molecular concentration and viscoelastic property mapping.
• Performed subcellular resolution imaging in living cells.
• Tracked lipid localization and concentration during the cell cycle.

Main Results:

• Identified phosphatidylcholine-type lipids specifically enriched in heterochromatin.
• Demonstrated a correlation between lipid concentration and heterochromatin's mechanical properties.
• Observed lipid absence in mitotic chromosomes and reappearance in early G1 phase heterochromatin.

Conclusions:

• Phosphatidylcholine lipids are key contributors to heterochromatin physical condensation.
• Lipid incorporation into heterochromatin is a regulated, cell-cycle-dependent process.
• Simultaneous Raman-Brillouin imaging provides a powerful tool to link chemical composition with cellular mechanics.